• Saurabh D Rindani

Articles written in Pramana – Journal of Physics

• γγ processes at high energypp colliders

• Beyond the standard model: Working group report

This report summarises the activities of the working group on ‘Physics beyond the Standard Model’. The results of investigations in incorporatingR-parity in grand unification, the possibility of a light charged Higgs boson in extension of MSSM and radiative generation of neutral vector boson self-couplings within the MSSM are described. Also given is an account of activities in neutrino physics, namely a proposal for a study of the atmospheric muon anomaly in deep underground mines, a field theoretic study of neutrino oscillations and a mechanism to generate appropriate masses of three active plus one sterile neutrino species.

• CP-violating dipole form factors of the top quark and tau lepton in scalar leptoquark models

We calculate the CP-violating electric and weak dipole form factors of the top quark and the tau lepton in models with scalar leptoquarks coupling only to the third generation of quarks and leptons. We obtain numerical values of the real and imaginary parts of these form factors at various energies for different values of leptoquark masses and couplings. The existing limits on the tau electric and weak dipole form factors allow us to put a limit on the masses and couplings of such leptoquarks and therefore on the top electric and weak dipole form factors. We also discuss constraints on the form factors coming from indirect limits on leptoquark masses and couplings deduced from LEP results on Z properties.

• Single decay-lepton angular distributions in polarizede+e →$$\overline {tt}$$ and simple angular asymmetries as a measure of CP-violating top dipole couplingsand simple angular asymmetries as a measure of CP-violating top dipole couplings

In the presence of an electric dipole coupling of$$\overline {tt}$$ to a photon, and an analogous ‘weak’ dipole coupling to the Z, CP violation in the process e+e →$$\overline {tt}$$ results in modified polarization of the top and the anti-top. This polarization can be analyzed by studying the angular distributions of decay charged leptons when the top or anti-top decays leptonically. Analytic expressions are presented for these distributions when eithert or$$\overline t$$ decays leptonically, including$$\mathcal{O}$$(αs) QCD corrections in the soft-gluon approximation. The angular distributions are insensitive to anomalous interactions in top decay. Two types of simple CP-violating polar-angle asymmetries and two azimuthal asymmetries, which do not need the full reconstruction of thet or$$\overline t$$, are studied. Independent 90% CL limits that may be obtained on the real and imaginary parts of the electric and weak dipole couplings at a linear collider operating at √ s = 500 GeV with integrated luminosity 500 fb and also at √s = 1000 GeV with integrated luminosity 1000 fb have been evaluated. The effect of longitudinal electron and/or positron beam polarizations has been included.

• Working group report: High energy and collider physics

This is a summary of the projects undertaken by the working group I on high energy and collider physics.

• Probing CP-violating Higgs contributions in $\gamma \gamma \rightarrow f\bar{f}$

We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson 𝜙 in $\gamma \gamma \rightarrow f\bar{f}$, $f = \tau/t$, from that of the QED continuum. This can help in getting information on the $\gamma \gamma \phi$ coupling in case 𝜙 is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case 𝜙 has indeterminate CP. Furthermore, we take the MSSM with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters.

• Transverse polarization in $\gamma Z; H Z$ production

With the use of transverse polarization (TP), a CP-odd and T-odd observable can be constructed when the final-state particles are self-conjugate. In the case of $H Z$ production, this observable can be used to probe a certain effective four-point $e^{+} e^{-} Z H$ CP-violating coupling, not accessible without TP. Effective CP-violating $Z Z H$ coupling does not contribute to this observable. A similar observable in $\gamma Z$ production can be used to probe $e^{+} e^{-} \gamma Z$ four-point couplings.

• Preface

• Top-spin analysis of new scalar and tensor interactions in $e^{+} e^{-}$ collisions with transverse beam polarization

The top polarization at the International Linear Collider (ILC) with transverse beam polarization is utilized in the $e^{+} e^{-} \rightarrow t\bar{t}$ process to probe interactions of the scalar and tensor type beyond the Standard Model and to disentangle their individual contributions. Confidence level limits of 90% are presented on the interactions with realistic integrated luminosity and are found to improve by an order of magnitude compared to the case when the spin of the top quark is not measured. Sensitivities of the order of a few times $10^{−3}$ TeV-2 for real and imaginary parts of both scalar and tensor couplings at $\sqrt{s} = 500$ and 800 GeV with an integrated luminosity of 500 fb-1 and completely polarized beams are shown to be possible.

• # Pramana – Journal of Physics

Current Issue
Volume 93 | Issue 5
November 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019